In the field of metallurgy, heat treatment is employed to achieve numerous results. In a broad sense heat treatment includes any thermal treatment intended to control properties. With respect to metal alloys, such as steel, tempering and annealing are particularly well known methods of heat treatment.
Heat treating to achieve a desired alteration of properties is often times a process that is performed optimally at a specific temperature. In order to maintain control over temperature during such heat treatment, temperature chambers and complex heater/thermostat arrangements are generally employed.
Typically, heat treating is performed before an article is sent to the field--the properties of the article being defined at the mill, factory, or other producing facility. However, at the time of installation of the article or after the article has been in use for a period of time, it may be deemed desirable to effectuate changes in the metallurgical properties of the article in the field, or in situ, without the need for a temperature chamber, oven or heater-thermostat arrangement. For example, where a pipe section along a pipeline is subject to cold temperatures and attendant degradation of properties, it is often desirable to service the pipe section by heat treatment in the field without the need for removing the section. Similarly, when stress, fatigue, or temperature adversely affect a section of pipe along a pipeline or a strut along a bridge or the like, heat treatment in the field is often desirable. In addition, steels exposed to heavy neutron irradiation are generally embrittled. Stress relief in situ is again often of great value.
In these and other situations, it is often found that only portions of an article require heat treatment and that, in fact, the heat treatment should be confined to only those portions and that those portions be heated to a uniform temperature. That is, it may be that only part of an article is to be hardened, softened, strengthened, stress-relieved, tempered, annealed, or otherwise treated--in which case it is desired that heat treating be localized.